1. Field of the Invention
The present invention relates to a cleaning device incorporated in an electrophotographic image forming apparatus such as a copier, a printer and a facsimile. More particularly, the present invention relates to a cleaning device for an image forming apparatus that uses high roundness toner to develop images.
2. Description of the Related Art
In order to enhance image quality, smaller diameter and higher roundness toner is being intensively designed at present. Since pulverized toner has limited characteristics on the toner diameter and the toner roundness thereof, polymerized toner manufactured, for example, in accordance with suspension polymerization, emulsion polymerization and dispersion polymerization, has been widely adopted to realize small diameter and high roundness toner.
It is known by those skilled in the art that high roundness toner has a poor cleaning characteristic in general. This is why when such high roundness toner is cleaned up with a rubber blade, which is conventionally used as means for cleaning pulverized toner, it is difficult for the rubber blade to catch the high roundness toner particles at the blade edge thereof because of tumbling of the round particles. As a result, the high roundness toner particles tend to pass through the rubber blade. In particular, since polymerized toner particles are shaped as true round particles (having average roundness above 0.98), it is difficult to properly clean up such high roundness toner particles in conventional blade cleaning methods as described above.
Some cleaning methods for high roundness toner have been proposed as follows.
Japanese Laid-Open Patent Application No. 08-248849 discloses a method of removing toner particles electrostatically from an image support body by means of a brush roller by applying bias having inverse polarity of toner electrifying polarity to the brush roller. However, the method has some problems. Typically, since remaining toner particles are not uniformly electrified on the image support body, it is difficult for the uniformly bias-applied brush roller to successfully catch the remaining toners from the image support body. Also, there is a risk that the caught toner particles may be reattached on the image support body depending on the level of the applied bias.
There are some other approaches. In a proposed cleaning method, for the purpose of improving cleaning performance of a rubber blade, the friction coefficient of the surface of an image support body can be lowered by supplying an antifriction material on the surface. In this method, even if greater depression force of a rubber blade is applied to the image support body in order to scrape remaining toner particles from the image support body, it is possible to suppress damage to the image support body. In addition, it is possible to improve cleaning performance of the rubber blade by lowering the coefficient of sliding friction of the toner particles.
Japanese Laid-Open Patent Applications No. 11-288194 and No. 2001-235987 disclose methods of supplying an antifriction material on an image support body. In these methods, a solid antifriction material is applied to a brush roller disposed in the upstream side from a rubber blade with respect to the rotational direction of an image support body so that the brush roller can clean up the surface of the image support body. At the same time, the solid antifriction material is scraped while supplying the antifriction material on the image support body. According to the above-proposed methods, however, when toner particles are accumulated between fibers of a brush roller over time, there is a risk that an antifriction material scraped by the brush roller cannot be sufficiently supplied on the image support body.